An mRNA is 429 nucleotides long. The number of amino acids in the polypeptide chain formed from this mRNA is:
(A) 143
(B) 142
(C) 141
(D) 429
(E) 428
Answer (3)
B. 142. This is because one of the molecules has to be a stop codon which doesn't code for an amino acid. So there are only 426 nucleotides coding for the polypeptide chain. It takes 3 nucleotides to code for an amino acid. So 426 divided by 3 is 142, which is the amount of amino acids that will be part of this chain.
An mRNA of 429 nucleotides will form a polypeptide chain with 143 amino acids, assuming each codon (set of 3 nucleotides) corresponds to an amino acid and the stop codon is not counted. ;
An mRNA that is 429 nucleotides long produces a polypeptide chain with 143 amino acids, since each amino acid corresponds to a codon made up of three nucleotides. Therefore, the chosen answer is (A) 143.
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